Changing the order of a string based on an array of numbers in C#

Thanks for the help with my question about making an array of booleans into a str开发者_高级运维ing. The code is now working good. Now I have another problem. Maybe somebody would like to try. I think I could come up with a solution but if so I'm 99 percent sure that it would be not so simple as the answers I have seen from people here.

What I have is the string "ABD" from my question here. I also have an array of integers. For example [0] = 2, [1] = 3 and [2] = 1. I would like to find a way to apply this to my string to reorder the string so that the string changes to BDA.

Can anyone think of a simple way to do this?

If those integers are 1-based indices within the string (i.e. 2 = 2nd character), then you could do this:

string s = "ABD";
int[] oneBasedIndices = new [] { 2, 3, 1 };

string result = String.Join(String.Empty, oneBasedIndices.Select(i => s[i-1]));

NB: If you are using a version less than C# 4.0, you need to put a .ToArray() on the end of the select.

What this is doing is going through your int[] and with each int element picking the character in the string at that position (well -1, as the first index in an array is 0, but your example starts at 1).

Then, it has to do a String.Join() to turn that collection of characters back into a String.

As an aside, I'd recommend downloading LINQPad (no connection) - then you can just paste that code in there as a C# Program, and at any point type variable.Dump(); (e.g. result.Dump(); at the end) and see what the value is at that point.

First make a copy of the string. The copy will never change; it serves as your reference to what the values used to be.

Then loop through the original string one character at a time using a for loop. The counter in the for loop is the position of which character in the original string we are replacing next. The counter is also the index into the array to look up the position in the original string. Then replace the character at that position in the original string with the character from the copied string.

string orig = "ABD";
int[] oneBasedIndices = new [] { 2, 3, 1 };

string copy = orig;
for ( int i = 0; i < orig.Length; i++ )
{
    orig[i] = copy[ oneBasedIndices[i] - 1 ];
}

There you have it. If the indices are zero based, remove the - 1.

Napkin code again...

    string result = "ABD"; // from last question
    var indecies = new []{ 1,2,0 };

    string result2 = indecies.Aggregate(new StringBuilder(), 
       (sb, i)=>sb.Append(result[i]))
       .ToString();

or a different version (in hopes of redeeming myself for -1)

StringBuilder sb = new StringBuilder();
for(int i = 0; i < indecies.Length; i++)
{
   sb.Append(result[i]); // make [i-1] if indecies are 1 based.
}
string result3 = sb.ToString();